The use of short interconnections normal to the surfaces of circuit boards (Z-interconnections) is one method to desirably create space saving multi-layer circuit board configurations. For example, in sufficiently complex devices, the number and complexity of the desired interconnections may make the use of a multiple layer circuit board design desirable. Matrix array devices, such as are often found in pixel-based detector and display applications, may also desirably include multiple circuit board configurations coupled using Z-interconnections.
Area array electrical Z-interconnections over relatively large areas (squares of 4 to 6 inches per side) may be particularly desirable to build display modules that could be utilized in the construction of large-area seamless displays, or relatively large area, high-resolution detector arrays. For seamless integration, it is desirable for all electrical connections from the display panel (device in this application) to the circuit board to be made within the space between the device and the circuit board, because the device is covered with display elements almost all the way to the edges. There may be insufficient inactive area at the edges of the device for electrical connections.
Therefore, low cost circuit board materials and processes for forming substantially identical Z-interconnections throughout the large area module are desirable. Achieving high yields and long-term reliability of those interconnections are also desirable.
For example, in the current fabrication of displays based on organic light emitting diode (OLED) as the active element, it is sometimes considered necessary to hermetically seal the circuit board to the device. This is because the primary passivation on the device provided by some device manufacturers are not adequate. Therefore, display module manufacturers use more expensive rigid inorganic circuit board materials such as multi-layer alumina ceramic board that can provide a hermetic cover to the device. A sequential screen printing of conducting (noble metal) layers and insulating layers on a pre-fired, laser-drilled alumina ceramic is used to achieve the circuit precision needed for large area circuits. Due to the relatively lower circuit density of these boards, several layers of metallization may be needed to accomplish the needed circuit routing. These factors result in high materials and production cost in making these circuit boards for back panel applications.